Method of Formulating Perovskite Solar Cell Materials

ABSTRACT

A method for preparing photoactive perovskite materials. The method comprises the step of preparing a lead halide precursor ink. Preparing a lead halide precursor ink comprises the steps of: introducing a lead halide into a vessel, introducing a first solvent to the vessel, and contacting the lead halide with the first solvent to dissolve the lead halide. The method further comprises depositing the lead halide precursor ink onto a substrate, drying the lead halide precursor ink to form a thin film, annealing the thin film, and rinsing the thin film with a second solvent and a salt.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/711,330 filed May 13, 2015 and entitled “Method of FormulatingPerovskite Solar Cell Materials,” which is based upon and claimspriority to U.S. Provisional Patent Application Ser. No. 62/032,137,entitled “Method of Formulating Perovskite Solar Cell Materials,” filedAug. 1, 2014.

BACKGROUND

Use of photovoltaics (PVs) to generate electrical power from solarenergy or radiation may provide many benefits, including, for example, apower source, low or zero emissions, power production independent of thepower grid, durable physical structures (no moving parts), stable andreliable systems, modular construction, relatively quick installation,safe manufacture and use, and good public opinion and acceptance of use.

The features and advantages of the present disclosure will be readilyapparent to those skilled in the art. While numerous changes may be madeby those skilled in the art, such changes are within the spirit of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of DSSC design depicting various layers of theDSSC according to some embodiments of the present disclosure.

FIG. 2 is another illustration of DSSC design depicting various layersof the DSSC according to some embodiments of the present disclosure.

FIG. 3 is an example illustration of BHJ device design according to someembodiments of the present disclosure.

FIG. 4 is a schematic view of a typical photovoltaic cell including anactive layer according to some embodiments of the present disclosure.

FIG. 5 is a schematic of a typical solid state DSSC device according tosome embodiments of the present disclosure.

FIG. 6 is a stylized diagram illustrating components of an exemplar PVdevice according to some embodiments of the present disclosure.

FIG. 7 is a stylized diagram showing components of an exemplar PV deviceaccording to some embodiments of the present disclosure.

FIG. 8 is a stylized diagram showing components of an exemplar PV deviceaccording to some embodiments of the present disclosure.

FIG. 9 is a stylized diagram showing components of an exemplar PV deviceaccording to some embodiments of the present disclosure.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Improvements in various aspects of PV technologies compatible withorganic, non-organic, and/or hybrid PVs promise to further lower thecost of both OPVs and other PVs. For example, some solar cells, such assolid-state dye-sensitized solar cells, may take advantage of novelcost-effective and high-stability alternative components, such assolid-state charge transport materials (or, colloquially, “solid stateelectrolytes”). In addition, various kinds of solar cells mayadvantageously include interfacial and other materials that may, amongother advantages, be more cost-effective and durable than conventionaloptions currently in existence.

The present disclosure relates generally to compositions of matter,apparatus and methods of use of materials in photovoltaic cells increating electrical energy from solar radiation. More specifically, thisdisclosure relates to photoactive and other compositions of matter, aswell as apparatus, methods of use, and formation of such compositions ofmatter.

Examples of these compositions of matter may include, for example,hole-transport materials, and/or materials that may be suitable for useas, e.g., interfacial layers, dyes, and/or other elements of PV devices.Such compounds may be deployed in a variety of PV devices, such asheterojunction cells (e.g., bilayer and bulk), hybrid cells (e.g.,organics with CH₃NH₃PbI₃, ZnO nanorods or PbS quantum dots), and DSSCs(dye-sensitized solar cells). The latter, DSSCs, exist in three forms:solvent-based electrolytes, ionic liquid electrolytes, and solid-statehole transporters (or solid-state DSSCs, i.e., SS-DSSCs). SS-DSSCstructures according to some embodiments may be substantially free ofelectrolyte, containing rather hole-transport materials such asspiro-OMeTAD, CsSnI₃, and other active materials.

Some or all of materials in accordance with some embodiments of thepresent disclosure may also advantageously be used in any organic orother electronic device, with some examples including, but not limitedto: batteries, field-effect transistors (FETs), light-emitting diodes(LEDs), non-linear optical devices, memristors, capacitors, rectifiers,and/or rectifying antennas.

In some embodiments, the present disclosure may provide PV and othersimilar devices (e.g., batteries, hybrid PV batteries, multi-junctionPVs, FETs, LEDs etc.). Such devices may in some embodiments includeimproved active material, interfacial layers, and/or one or moreperovskite materials. A perovskite material may be incorporated intovarious of one or more aspects of a PV or other device. A perovskitematerial according to some embodiments may be of the general formulaCMX3, where: C comprises one or more cations (e.g., an amine, ammonium,a Group 1 metal, a Group 2 metal, and/or other cations or cation-likecompounds); M comprises one or more metals (exemplars including Fe, Co,Ni, Cu, Sn, Pb, Bi, Ge, Ti, and Zr); and X comprises one or more anions.Perovskite materials according to various embodiments are discussed ingreater detail below.

Photovoltaic Cells and Other Electronic Devices

Some PV embodiments may be described by reference to variousillustrative depictions of solar cells as shown in FIGS. 1, 3, 4, and 5.For example, an exemplary PV architecture according to some embodimentsmay be substantially of the form substrate-anode-IFL-activelayer-IFL-cathode. The active layer of some embodiments may bephotoactive, and/or it may include photoactive material. Other layersand materials may be utilized in the cell as is known in the art.Furthermore, it should be noted that the use of the term “active layer”is in no way meant to restrict or otherwise define, explicitly orimplicitly, the properties of any other layer—for instance, in someembodiments, either or both IFLs may also be active insofar as they maybe semiconducting. In particular, referring to FIG. 4, a stylizedgeneric PV cell 2610 is depicted, illustrating the highly interfacialnature of some layers within the PV. The PV 2610 represents a genericarchitecture applicable to several PV devices, such as DSSC PVembodiments. The PV cell 2610 includes a transparent layer 2612 of glass(or material similarly transparent to solar radiation) which allowssolar radiation 2614 to transmit through the layer. The transparentlayer of some embodiments may also be referred to as a substrate (e.g.,as with substrate layer 1507 of FIG. 1), and it may comprise any one ormore of a variety of rigid or flexible materials such as: glass,polyethylene, PET, Kapton, quartz, aluminum foil, gold foil, or steel.The photoactive layer 2616 is composed of electron donor or p-typematerial 2618 and electron acceptor or n-type material 2620. The activelayer or, as depicted in FIG. 4, the photoactive layer 2616, issandwiched between two electrically conductive electrode layers 2622 and2624. In FIG. 4, the electrode layer 2622 is an ITO material. Aspreviously noted, an active layer of some embodiments need notnecessarily be photoactive, although in the device shown in FIG. 4, itis. The electrode layer 2624 is an aluminum material. Other materialsmay be used as is known in the art. The cell 2610 also includes aninterfacial layer (IFL) 2626, shown in the example of FIG. 4 as aPEDOT:PSS material. The IFL may assist in charge separation. In someembodiments, the IFL 2626 may comprise a photoactive organic compoundaccording to the present disclosure as a self-assembled monolayer (SAM)or as a thin film. In other embodiments, the IFL 2626 may comprise athin-coat bilayer, which is discussed in greater detail below. Therealso may be an IFL 2627 on the aluminum-cathode side of the device. Insome embodiments, the IFL 2627 on the aluminum-cathode side of thedevice may also or instead comprise a photoactive organic compoundaccording to the present disclosure as a self-assembled monolayer (SAM)or as a thin film. In other embodiments, the IFL 2627 on thealuminum-cathode side of the device may also or instead comprise athin-coat bilayer (again, discussed in greater detail below). An IFLaccording to some embodiments may be semiconducting in character, andmay be either p-type or n-type. In some embodiments, the IFL on thecathode side of the device (e.g., IFL 2627 as shown in FIG. 4) may bep-type, and the IFL on the anode side of the device (e.g., IFL 2626 asshown in FIG. 4) may be n-type. In other embodiments, however, thecathode-side IFL may be n-type and the anode-side IFL may be p-type. Thecell 2610 is attached to leads 2630 and a discharge unit 2632, such as abattery.

Yet further embodiments may be described by reference to FIG. 3, whichdepicts a stylized BHJ device design, and includes: glass substrate2401; ITO (tin-doped indium oxide) electrode 2402; interfacial layer(IFL) 2403; photoactive layer 2404; and LiF/Al cathodes 2405. Thematerials of BHJ construction referred to are mere examples; any otherBHJ construction known in the art may be used consistent with thepresent disclosure. In some embodiments, the photoactive layer 2404 maycomprise any one or more materials that the active or photoactive layer2616 of the device of FIG. 4 may comprise.

FIG. 1 is a simplified illustration of DSSC PVs according to someembodiments, referred to here for purposes of illustrating assembly ofsuch example PVs. An example DSSC as shown in FIG. 1 may be constructedaccording to the following: electrode layer 1506 (shown asfluorine-doped tin oxide, FTO) is deposited on a substrate layer 1507(shown as glass). Mesoporous layer ML 1505 (which may in someembodiments be TiO₂) is deposited onto the electrode layer 1506, thenthe photoelectrode (so far comprising substrate layer 1507, electrodelayer 1506, and mesoporous layer 1505) is soaked in a solvent (notshown) and dye 1504. This leaves the dye 1504 bound to the surface ofthe ML. A separate counter-electrode is made comprising substrate layer1501 (also shown as glass) and electrode layer 1502 (shown as Pt/FTO).The photoelectrode and counter-electrode are combined, sandwiching thevarious layers 1502-1506 between the two substrate layers 1501 and 1507as shown in FIG. 1, and allowing electrode layers 1502 and 1506 to beutilized as a cathode and anode, respectively. A layer of electrolyte1503 is deposited either directly onto the completed photoelectrodeafter dye layer 1504 or through an opening in the device, typically ahole pre-drilled by sand-blasting in the counter-electrode substrate1501. The cell may also be attached to leads and a discharge unit, suchas a battery (not shown). Substrate layer 1507 and electrode layer 1506,and/or substrate layer 1501 and electrode layer 1502 should be ofsufficient transparency to permit solar radiation to pass through to thephotoactive dye 1504. In some embodiments, the counter-electrode and/orphotoelectrode may be rigid, while in others either or both may beflexible. The substrate layers of various embodiments may comprise anyone or more of: glass, polyethylene, PET, Kapton, quartz, aluminum foil,gold foil, and steel. In certain embodiments, a DSSC may further includea light harvesting layer 1601, as shown in FIG. 2, to scatter incidentlight in order to increase the light's path length through thephotoactive layer of the device (thereby increasing the likelihood thelight is absorbed in the photoactive layer).

In other embodiments, the present disclosure provides solid state DSSCs.Solid-state DSSCs according to some embodiments may provide advantagessuch as lack of leakage and/or corrosion issues that may affect DSSCscomprising liquid electrolytes. Furthermore, a solid-state chargecarrier may provide faster device physics (e.g., faster chargetransport). Additionally, solid-state electrolytes may, in someembodiments, be photoactive and therefore contribute to power derivedfrom a solid-state DSSC device.

Some examples of solid state DSSCs may be described by reference to FIG.5, which is a stylized schematic of a typical solid state DSSC. As withthe example solar cell depicted in, e.g., FIG. 4, an active layercomprised of first and second active (e.g., conducting and/orsemi-conducting) material (2810 and 2815, respectively) is sandwichedbetween electrodes 2805 and 2820 (shown in FIG. 5 as Pt/FTO and FTO,respectively). In the embodiment shown in FIG. 5, the first activematerial 2810 is p-type active material, and comprises a solid-stateelectrolyte. In certain embodiments, the first active material 2810 maycomprise an organic material such as spiro-OMeTAD and/orpoly(3-hexylthiophene), an inorganic binary, ternary, quaternary, orgreater complex, any solid semiconducting material, or any combinationthereof. In some embodiments, the first active material may additionallyor instead comprise an oxide and/or a sulfide, and/or a selenide, and/oran iodide (e.g., CsSnI₃). Thus, for example, the first active materialof some embodiments may comprise solid-state p-type material, which maycomprise copper indium sulfide, and in some embodiments, it may comprisecopper indium gallium selenide. The second active material 2815 shown inFIG. 5 is n-type active material and comprises TiO₂ coated with a dye.In some embodiments, the second active material may likewise comprise anorganic material such as spiro-OMeTAD, an inorganic binary, ternary,quaternary, or greater complex, or any combination thereof. In someembodiments, the second active material may comprise an oxide such asalumina, and/or it may comprise a sulfide, and/or it may comprise aselenide. Thus, in some embodiments, the second active material maycomprise copper indium sulfide, and in some embodiments, it may comprisecopper indium gallium selenide metal. The second active material 2815 ofsome embodiments may constitute a mesoporous layer. Furthermore, inaddition to being active, either or both of the first and second activematerials 2810 and 2815 may be photoactive. In other embodiments (notshown in FIG. 5), the second active material may comprise a solidelectrolyte. In addition, in embodiments where either of the first andsecond active material 2810 and 2815 comprise a solid electrolyte, thePV device may lack an effective amount of liquid electrolyte. Althoughshown and referred to in FIG. 5 as being p-type, a solid state layer(e.g., first active material comprising solid electrolyte) may in someembodiments instead be n-type semiconducting. In such embodiments, then,the second active material (e.g., TiO₂ (or other mesoporous material) asshown in FIG. 5) coated with a dye may be p-type semiconducting (asopposed to the n-type semiconducting shown in, and discussed withrespect to, FIG. 5).

Substrate layers 2801 and 2825 (both shown in FIG. 5 as glass) form therespective external top and bottom layers of the exemplar cell of FIG.5. These layers may comprise any material of sufficient transparency topermit solar radiation to pass through to the active/photoactive layercomprising dye, first and second active and/or photoactive material 2810and 2815, such as glass, polyethylene, PET, Kapton, quartz, aluminumfoil, gold foil, and/or steel. Furthermore, in the embodiment shown inFIG. 5, electrode 2805 (shown as Pt/FTO) is the cathode, and electrode2820 is the anode. As with the exemplar solar cell depicted in FIG. 4,solar radiation passes through substrate layer 2825 and electrode 2820into the active layer, whereupon at least a portion of the solarradiation is absorbed so as to produce one or more excitons to enableelectrical generation.

A solid state DSSC according to some embodiments may be constructed in asubstantially similar manner to that described above with respect to theDSSC depicted as stylized in FIG. 1. In the embodiment shown in FIG. 5,p-type active material 2810 corresponds to electrolyte 1503 of FIG. 1;n-type active material 2815 corresponds to both dye 1504 and ML 1505 ofFIG. 1; electrodes 2805 and 2820 respectively correspond to electrodelayers 1502 and 1506 of FIG. 1; and substrate layers 2801 and 2825respectively correspond to substrate layers 1501 and 1507.

Various embodiments of the present disclosure provide improved materialsand/or designs in various aspects of solar cell and other devices,including among other things, active materials (including hole-transportand/or electron-transport layers), interfacial layers, and overalldevice design.

Interfacial Layers

The present disclosure in some embodiments provides advantageousmaterials and designs of one or more interfacial layers within a PV,including thin-coat IFLs. Thin-coat IFLs may be employed in one or moreIFLs of a PV according to various embodiments discussed herein.

First, as previously noted, one or more IFLs (e.g., either or both IFLs2626 and 2627 as shown in FIG. 4) may comprise a photoactive organiccompound of the present disclosure as a self-assembled monolayer (SAM)or as a thin film. When a photoactive organic compound of the presentdisclosure is applied as a SAM, it may comprise a binding group throughwhich it may be covalently or otherwise bound to the surface of eitheror both of the anode and cathode. The binding group of some embodimentsmay comprise any one or more of COOH, SiX₃ (where X may be any moietysuitable for forming a ternary silicon compound, such as Si(OR)₃ andSiCl₃), SO₃, PO₄H, OH, CH₂X (where X may comprise a Group 17 halide),and O. The binding group may be covalently or otherwise bound to anelectron-withdrawing moiety, an electron donor moiety, and/or a coremoiety. The binding group may attach to the electrode surface in amanner so as to form a directional, organized layer of a single molecule(or, in some embodiments, multiple molecules) in thickness (e.g., wheremultiple photoactive organic compounds are bound to the anode and/orcathode). As noted, the SAM may attach via covalent interactions, but insome embodiments it may attach via ionic, hydrogen-bonding, and/ordispersion force (i.e., Van Der Waals) interactions. Furthermore, incertain embodiments, upon light exposure, the SAM may enter into azwitterionic excited state, thereby creating a highly-polarized IFL,which may direct charge carriers from an active layer into an electrode(e.g., either the anode or cathode). This enhanced charge-carrierinjection may, in some embodiments, be accomplished by electronicallypoling the cross-section of the active layer and therefore increasingcharge-carrier drift velocities towards their respective electrode(e.g., hole to anode; electrons to cathode). Molecules for anodeapplications of some embodiments may comprise tunable compounds thatinclude a primary electron donor moiety bound to a core moiety, which inturn is bound to an electron-withdrawing moiety, which in turn is boundto a binding group. In cathode applications according to someembodiments, IFL molecules may comprise a tunable compound comprising anelectron poor moiety bound to a core moiety, which in turn is bound toan electron donor moiety, which in turn is bound to a binding group.When a photoactive organic compound is employed as an IFL according tosuch embodiments, it may retain photoactive character, although in someembodiments it need not be photoactive.

In addition or instead of a photoactive organic compound SAM IFL, a PVaccording to some embodiments may include a thin interfacial layer (a“thin-coat interfacial layer” or “thin-coat IFL”) coated onto at least aportion of either the first or the second active material of suchembodiments (e.g., first or second active material 2810 or 2815 as shownin FIG. 5). And, in turn, at least a portion of the thin-coat IFL may becoated with a dye. The thin-coat IFL may be either n- or p-type; in someembodiments, it may be of the same type as the underlying material(e.g., TiO₂ or other mesoporous material, such as TiO₂ of second activematerial 2815). The second active material may comprise TiO₂ coated witha thin-coat IFL comprising alumina (e.g., Al₂O₃) (not shown in FIG. 5),which in turn is coated with a dye. References herein to TiO₂ and/ortitania are not intended to limit the ratios of tin and oxide in suchtin-oxide compounds described herein. That is, a titania compound maycomprise titanium in any one or more of its various oxidation states(e.g., titanium I, titanium II, titanium III, titanium IV), and thusvarious embodiments may include stoichiometric and/or non-stoichiometricamounts of titanium and oxide. Thus, various embodiments may include(instead or in addition to TiO₂) Ti_(x)O_(y), where x may be any value,integer or non-integer, between 1 and 100. In some embodiments, x may bebetween approximately 0.5 and 3. Likewise, y may be betweenapproximately 1.5 and 4 (and, again, need not be an integer). Thus, someembodiments may include, e.g., TiO₂ and/or Ti₂O₃. In addition, titaniain whatever ratios or combination of ratios between titanium and oxidemay be of any one or more crystal structures in some embodiments,including any one or more of anatase, rutile, and amorphous.

Other exemplar metal oxides for use in the thin-coat IFL of someembodiments may include semiconducting metal oxides, such as ZnO, ZrO₂,Nb₂O₃, SrTiO₃, Ta₂O₃, NiO, WO₃, V₂O₅, or MoO₃. The exemplar embodimentwherein the second (e.g., n-type) active material comprises TiO₂ coatedwith a thin-coat IFL comprising Al₂O₃ could be formed, for example, witha precursor material such as Al(NO₃)₃.xH₂O, or any other materialsuitable for depositing Al₂O₃ onto the TiO₂, followed by thermalannealing and dye coating. In example embodiments wherein a MoO₃ coatingis instead used, the coating may be formed with a precursor materialsuch as Na₂Mo₄.2H₂O; whereas a V₂O₅ coating according to someembodiments may be formed with a precursor material such as NaVO₃; and aWO₃ coating according to some embodiments may be formed with a precursormaterial such as NaWO₄.H₂O. The concentration of precursor material(e.g., Al(NO₃)₃.xH₂O) may affect the final film thickness (here, ofAl₂O₃) deposited on the TiO₂ or other active material. Thus, modifyingthe concentration of precursor material may be a method by which thefinal film thickness may be controlled. For example, greater filmthickness may result from greater precursor material concentration.Greater film thickness may not necessarily result in greater PCE in a PVdevice comprising a metal oxide coating. Thus, a method of someembodiments may include coating a TiO₂ (or other mesoporous) layer usinga precursor material having a concentration in the range ofapproximately 0.5 to 10.0 mM; other embodiments may include coating thelayer with a precursor material having a concentration in the range ofapproximately 2.0 to 6.0 mM; or, in other embodiments, approximately 2.5to 5.5 mM.

Furthermore, although referred to herein as Al₂O₃ and/or alumina, itshould be noted that various ratios of aluminum and oxygen may be usedin forming alumina. Thus, although some embodiments discussed herein aredescribed with reference to Al₂O₃, such description is not intended todefine a required ratio of aluminum in oxygen. Rather, embodiments mayinclude any one or more aluminum-oxide compounds, each having analuminum oxide ratio according to Al_(x)O_(y), where x may be any value,integer or non-integer, between approximately 1 and 100. In someembodiments, x may be between approximately 1 and 3 (and, again, neednot be an integer). Likewise, y may be any value, integer ornon-integer, between 0.1 and 100. In some embodiments, y may be between2 and 4 (and, again, need not be an integer). In addition, variouscrystalline forms of Al_(x)O_(y) may be present in various embodiments,such as alpha, gamma, and/or amorphous forms of alumina.

Likewise, although referred to herein as MoO₃, WO₃, and V₂O₅, suchcompounds may instead or in addition be represented as Mo_(x)O_(y),W_(x)O_(y), and V_(x)O_(y), respectively. Regarding each of Mo_(x)O_(y)and W_(x)O_(y), x may be any value, integer or non-integer, betweenapproximately 0.5 and 100; in some embodiments, it may be betweenapproximately 0.5 and 1.5. Likewise, y may be any value, integer ornon-integer, between approximately 1 and 100. In some embodiments, y maybe any value between approximately 1 and 4. Regarding V_(x)O_(y), x maybe any value, integer or non-integer, between approximately 0.5 and 100;in some embodiments, it may be between approximately 0.5 and 1.5.Likewise, y may be any value, integer or non-integer, betweenapproximately 1 and 100; in certain embodiments, it may be an integer ornon-integer value between approximately 1 and 10.

Similarly, references in some exemplar embodiments herein to CsSnI₃ arenot intended to limit the ratios of component elements in thecesium-tin-iodine compounds according to various embodiments. Someembodiments may include stoichiometric and/or non-stoichiometric amountsof tin and iodide, and thus such embodiments may instead or in additioninclude various ratios of cesium, tin, and iodine, such as any one ormore cesium-tin-iodine compounds, each having a ratio ofCs_(x)Sn_(y)I_(z). In such embodiments, x may be any value, integer ornon-integer, between 0.1 and 100. In some embodiments, x may be betweenapproximately 0.5 and 1.5 (and, again, need not be an integer) Likewise,y may be any value, integer or non-integer, between 0.1 and 100. In someembodiments, y may be between approximately 0.5 and 1.5 (and, again,need not be an integer). Likewise, z may be any value, integer ornon-integer, between 0.1 and 100. In some embodiments, z may be betweenapproximately 2.5 and 3.5. Additionally CsSnI₃ can be doped orcompounded with other materials, such as SnF₂, in ratios of CsSnI₃:SnF₂ranging from 0.1:1 to 100:1, including all values (integer andnon-integer) in between.

In addition, a thin-coat IFL may comprise a bilayer. Thus, returning tothe example wherein the thin-coat IFL comprises a metal-oxide (such asalumina), the thin-coat IFL may comprise TiO₂-plus-metal-oxide. Such athin-coat IFL may have a greater ability to resist charge recombinationas compared to mesoporous TiO₂ or other active material alone.Furthermore, in forming a TiO₂ layer, a secondary TiO₂ coating is oftennecessary in order to provide sufficient physical interconnection ofTiO₂ particles, according to some embodiments of the present disclosure.Coating a bilayer thin-coat IFL onto mesoporous TiO₂ (or othermesoporous active material) may comprise a combination of coating usinga compound comprising both metal oxide and TiCl₄, resulting in anbilayer thin-coat IFL comprising a combination of metal-oxide andsecondary TiO₂ coating, which may provide performance improvements overuse of either material on its own.

The thin-coat IFLs and methods of coating them onto TiO₂ previouslydiscussed may, in some embodiments, be employed in DSSCs comprisingliquid electrolytes. Thus, returning to the example of a thin-coat IFLand referring back to FIG. 1 for an example, the DSSC of FIG. 1 couldfurther comprise a thin-coat IFL as described above coated onto themesoporous layer 1505 (that is, the thin-coat IFL would be insertedbetween mesoporous layer 1505 and dye 1504).

In some embodiments, the thin-coat IFLs previously discussed in thecontext of DSSCs may be used in any interfacial layer of a semiconductordevice such as a PV (e.g., a hybrid PV or other PV), field-effecttransistor, light-emitting diode, non-linear optical device, memristor,capacitor, rectifier, rectifying antenna, etc. Furthermore, thin-coatIFLs of some embodiments may be employed in any of various devices incombination with other compounds discussed in the present disclosure,including but not limited to any one or more of the following of variousembodiments of the present disclosure: solid hole-transport materialsuch as active material and additives (such as, in some embodiments,chenodeoxycholic acid or 1,8-diiodooctane).

Additives

As previously noted, PV and other devices according to some embodimentsmay include additives (which may be, e.g., any one or more of aceticacid, propanoic acid, trifluoroacetic acid, chenodeoxycholic acid,deoxycholic acid, 1,8-diiodooctane, and 1,8-dithiooctane). Suchadditives may be employed as pretreatments directly before dye soakingor mixed in various ratios with a dye to form the soaking solution.These additives may in some instances function, for example, to increasedye solubility, preventing dye molecule clustering, by blocking openactive sites, and by inducing molecular ordering amongst dye molecules.They may be employed with any suitable dye, including a photoactivecompound according to various embodiments of the present disclosure asdiscussed herein.

Perovskite Material

A perovskite material may be incorporated into various of one or moreaspects of a PV or other device. A perovskite material according to someembodiments may be of the general formula CMX₃, where: C comprises oneor more cations (e.g., an amine, ammonium, a Group 1 metal, a Group 2metal, and/or other cations or cation-like compounds); M comprises oneor more metals (exemplars including Fe, Co, Ni, Cu, Sn, Pb, Bi, Ge, Ti,and Zr); and X comprises one or more anions. In some embodiments, C mayinclude one or more organic cations.

In certain embodiments, C may include an ammonium, an organic cation ofthe general formula [NR₄]⁺ where the R groups can be the same ordifferent groups. Suitable R groups include, but are not limited to:methyl, ethyl, propyl, butyl, pentyl group or isomer thereof; anyalkane, alkene, or alkyne CxHy, where x=1-20, y=1-42, cyclic, branchedor straight-chain; alkyl halides, CxHyXz, x=1-20, y=0-42, z=1-42, X═F,Cl, Br, or I; any aromatic group (e.g., phenyl, alkylphenyl,alkoxyphenyl, pyridine, naphthalene); cyclic complexes where at leastone nitrogen is contained within the ring (e.g., pyridine, pyrrole,pyrrolidine, piperidine, tetrahydroquinoline); any sulfur-containinggroup (e.g., sulfoxide, thiol, alkyl sulfide); any nitrogen-containinggroup (nitroxide, amine); any phosphorous containing group (phosphate);any boron-containing group (e.g., boronic acid); any organic acid (e.g.,acetic acid, propanoic acid); and ester or amide derivatives thereof;any amino acid (e.g., glycine, cysteine, proline, glutamic acid,arginine, serine, histindine, 5-ammoniumvaleric acid) including alpha,beta, gamma, and greater derivatives; any silicon containing group(e.g., siloxane); and any alkoxy or group, —OCxHy, where x=0-20, y=1-42.

In certain embodiments, C may include a formamidinium, an organic cationof the general formula [R₂NCHNR₂]⁺ where the R groups can be the same ordifferent groups. Suitable R groups include, but are not limited to:hydrogen, methyl, ethyl, propyl, butyl, pentyl group or isomer thereof;any alkane, alkene, or alkyne CxHy, where x=1-20, y=1-42, cyclic,branched or straight-chain; alkyl halides, CxHyXz, x=1-20, y=0-42,z=1-42, X═F, Cl, Br, or I; any aromatic group (e.g., phenyl,alkylphenyl, alkoxyphenyl, pyridine, naphthalene); cyclic complexeswhere at least one nitrogen is contained within the ring (e.g.,imidazole, benzimidazole, dihydropyrimidine,(azolidinylidenemethyl)pyrrolidine, triazole); any sulfur-containinggroup (e.g., sulfoxide, thiol, alkyl sulfide); any nitrogen-containinggroup (nitroxide, amine); any phosphorous containing group (phosphate);any boron-containing group (e.g., boronic acid); any organic acid(acetic acid, propanoic acid) and ester or amide derivatives thereof;any amino acid (e.g., glycine, cysteine, proline, glutamic acid,arginine, serine, histindine, 5-ammoniumvaleric acid) including alpha,beta, gamma, and greater derivatives; any silicon containing group(e.g., siloxane); and any alkoxy or group, —OCxHy, where x=0-20, y=1-42.

In certain embodiments, C may include a guanidinium, an organic cationof the general formula [(R₂N)₂C═NR₂]⁺ where the R groups can be the sameor different groups. Suitable R groups include, but are not limited to:hydrogen, methyl, ethyl, propyl, butyl, pentyl group or isomer thereof;any alkane, alkene, or alkyne CxHy, where x=1-20, y=1-42, cyclic,branched or straight-chain; alkyl halides, CxHyXz, x=1-20, y=0-42,z=1-42, X═F, Cl, Br, or I; any aromatic group (e.g., phenyl,alkylphenyl, alkoxyphenyl, pyridine, naphthalene); cyclic complexeswhere at least one nitrogen is contained within the ring (e.g.,octahydropyrimido[1,2-a]pyrimidine, pyrimido[1,2-a]pyrimidine,hexahydroimidazo[1,2-a]imidazole, hexahydropyrimidin-2-imine); anysulfur-containing group (e.g., sulfoxide, thiol, alkyl sulfide); anynitrogen-containing group (nitroxide, amine); any phosphorous containinggroup (phosphate); any boron-containing group (e.g., boronic acid); anyorganic acid (acetic acid, propanoic acid) and ester or amidederivatives thereof; any amino acid (e.g., glycine, cysteine, proline,glutamic acid, arginine, serine, histindine, 5-ammoniumvaleric acid)including alpha, beta, gamma, and greater derivatives; any siliconcontaining group (e.g., siloxane); and any alkoxy or group, —OCxHy,where x=0-20, y=1-42.

In certain embodiments, C may include an ethene tetramine cation, anorganic cation of the general formula [(R₂N)₂C═C(NR₂)₂]⁺ where the Rgroups can be the same or different groups. Suitable R groups include,but are not limited to: hydrogen, methyl, ethyl, propyl, butyl, pentylgroup or isomer thereof; any alkane, alkene, or alkyne CxHy, wherex=1-20, y=1-42, cyclic, branched or straight-chain; alkyl halides,CxHyXz, x=1-20, y=0-42, z=1-42, X═F, Cl, Br, or I; any aromatic group(e.g., phenyl, alkylphenyl, alkoxyphenyl, pyridine, naphthalene); cycliccomplexes where at least one nitrogen is contained within the ring(e.g., 2-hexahydropyrimidin-2-ylidenehexahydropyrimidine,octahydropyrazino[2,3-b]pyrazine, pyrazino[2,3-b]pyrazine,quinoxalino[2,3-b]quinoxaline); any sulfur-containing group (e.g.,sulfoxide, thiol, alkyl sulfide); any nitrogen-containing group(nitroxide, amine); any phosphorous containing group (phosphate); anyboron-containing group (e.g., boronic acid); any organic acid (aceticacid, propanoic acid) and ester or amide derivatives thereof; any aminoacid (e.g., glycine, cysteine, proline, glutamic acid, arginine, serine,histindine, 5-ammoniumvaleric acid) including alpha, beta, gamma, andgreater derivatives; any silicon containing group (e.g., siloxane); andany alkoxy or group, —OCxHy, where x=0-20, y=1-42.

In some embodiments, X may include one or more halides. In certainembodiments, X may instead or in addition include a Group 16 anion. Incertain embodiments, the Group 16 anion may be sulfide or selenide. Insome embodiments, each organic cation C may be larger than each metal M,and each anion X may be capable of bonding with both a cation C and ametal M. Examples of perovskite materials according to variousembodiments include CsSnI₃ (previously discussed herein) andCs_(x)Sn_(y)I_(z) (with x, y, and z varying in accordance with theprevious discussion). Other examples include compounds of the generalformula CsSnX₃, where X may be any one or more of: I₃, I_(2.95)F_(0.05);I₂Cl; ICl₂; and Cl₃. In other embodiments, X may comprise any one ormore of I, Cl, F, and Br in amounts such that the total ratio of X ascompared to Cs and Sn results in the general stoichiometry of CsSnX₃. Insome embodiments, the combined stoichiometry of the elements thatconstitute X may follow the same rules as I_(z) as previously discussedwith respect to Cs_(x)Sn_(y)I_(z). Yet other examples include compoundsof the general formula RNH₃PbX₃, where R may be C_(n)H_(2n+1), with nranging from 0-10, and X may include any one or more of F, Cl, Br, and Iin amounts such that the total ratio of X as compared to the cation RNH₃and metal Pb results in the general stoichiometry of RNH₃PbX₃. Further,some specific examples of R include H, alkyl chains (e.g., CH₃, CH₃CH₂,CH₃CH₂CH₂, and so on), and amino acids (e.g., glycine, cysteine,proline, glutamic acid, arginine, serine, histindine, 5-ammoniumvalericacid) including alpha, beta, gamma, and greater derivatives.

Composite Perovskite Material Device Design

In some embodiments, the present disclosure may provide composite designof PV and other similar devices (e.g., batteries, hybrid PV batteries,FETs, LEDs etc.) including one or more perovskite materials. Forexample, one or more perovskite materials may serve as either or both offirst and second active material of some embodiments (e.g., activematerials 2810 and 2815 of FIG. 5). In more general terms, someembodiments of the present disclosure provide PV or other devices havingan active layer comprising one or more perovskite materials. In suchembodiments, perovskite material (that is, material including any one ormore perovskite materials(s)) may be employed in active layers ofvarious architectures. Furthermore, perovskite material may serve thefunction(s) of any one or more components of an active layer (e.g.,charge transport material, mesoporous material, photoactive material,and/or interfacial material, each of which is discussed in greaterdetail below). In some embodiments, the same perovskite materials mayserve multiple such functions, although in other embodiments, aplurality of perovskite materials may be included in a device, eachperovskite material serving one or more such functions. In certainembodiments, whatever role a perovskite material may serve, it may beprepared and/or present in a device in various states. For example, itmay be substantially solid in some embodiments. In other embodiments, itmay be a solution (e.g., perovskite material may be dissolved in liquidand present in said liquid in its individual ionic subspecies); or itmay be a suspension (e.g., of perovskite material particles). A solutionor suspension may be coated or otherwise deposited within a device(e.g., on another component of the device such as a mesoporous,interfacial, charge transport, photoactive, or other layer, and/or on anelectrode). Perovskite materials in some embodiments may be formed insitu on a surface of another component of a device (e.g., by vapordeposition as a thin-film solid). Any other suitable means of forming asolid or liquid layer comprising perovskite material may be employed.

In general, a perovskite material device may include a first electrode,a second electrode, and an active layer comprising a perovskitematerial, the active layer disposed at least partially between the firstand second electrodes. In some embodiments, the first electrode may beone of an anode and a cathode, and the second electrode may be the otherof an anode and cathode. An active layer according to certainembodiments may include any one or more active layer components,including any one or more of: charge transport material; liquidelectrolyte; mesoporous material; photoactive material (e.g., a dye,silicon, cadmium telluride, cadmium sulfide, cadmium selenide, copperindium gallium selenide, gallium arsenide, germanium indium phosphide,semiconducting polymers, other photoactive materials)); and interfacialmaterial. Any one or more of these active layer components may includeone or more perovskite materials. In some embodiments, some or all ofthe active layer components may be in whole or in part arranged insub-layers. For example, the active layer may comprise any one or moreof: an interfacial layer including interfacial material; a mesoporouslayer including mesoporous material; and a charge transport layerincluding charge transport material. In some embodiments, photoactivematerial such as a dye may be coated on, or otherwise disposed on, anyone or more of these layers. In certain embodiments, any one or morelayers may be coated with a liquid electrolyte. Further, an interfaciallayer may be included between any two or more other layers of an activelayer according to some embodiments, and/or between a layer and acoating (such as between a dye and a mesoporous layer), and/or betweentwo coatings (such as between a liquid electrolyte and a dye), and/orbetween an active layer component and an electrode. Reference to layersherein may include either a final arrangement (e.g., substantiallydiscrete portions of each material separately definable within thedevice), and/or reference to a layer may mean arrangement duringconstruction of a device, notwithstanding the possibility of subsequentintermixing of material(s) in each layer. Layers may in some embodimentsbe discrete and comprise substantially contiguous material (e.g., layersmay be as stylistically illustrated in FIG. 1). In other embodiments,layers may be substantially intermixed (as in the case of, e.g., BHJ,hybrid, and some DSSC cells), an example of which is shown by first andsecond active material 2618 and 2620 within photoactive layer 2616 inFIG. 4. In some embodiments, a device may comprise a mixture of thesetwo kinds of layers, as is also shown by the device of FIG. 4, whichcontains discrete contiguous layers 2627, 2626, and 2622, in addition toa photoactive layer 2616 comprising intermixed layers of first andsecond active material 2618 and 2620. In any case, any two or morelayers of whatever kind may in certain embodiments be disposed adjacentto each other (and/or intermixedly with each other) in such a way as toachieve a high contact surface area. In certain embodiments, a layercomprising perovskite material may be disposed adjacent to one or moreother layers so as to achieve high contact surface area (e.g., where aperovskite material exhibits low charge mobility). In other embodiments,high contact surface area may not be necessary (e.g., where a perovskitematerial exhibits high charge mobility).

A perovskite material device according to some embodiments mayoptionally include one or more substrates. In some embodiments, eitheror both of the first and second electrode may be coated or otherwisedisposed upon a substrate, such that the electrode is disposedsubstantially between a substrate and the active layer. The materials ofcomposition of devices (e.g., substrate, electrode, active layer and/oractive layer components) may in whole or in part be either rigid orflexible in various embodiments. In some embodiments, an electrode mayact as a substrate, thereby negating the need for a separate substrate.

Furthermore, a perovskite material device according to certainembodiments may optionally include light-harvesting material (e.g., in alight-harvesting layer, such as Light Harvesting Layer 1601 as depictedin the exemplary PV represented in FIG. 2). In addition, a perovskitematerial device may include any one or more additives, such as any oneor more of the additives discussed above with respect to someembodiments of the present disclosure.

Description of some of the various materials that may be included in aperovskite material device will be made in part with reference to FIG.7. FIG. 7 is a stylized diagram of a perovskite material device 3900according to some embodiments. Although various components of the device3900 are illustrated as discrete layers comprising contiguous material,it should be understood that FIG. 7 is a stylized diagram; thus,embodiments in accordance with it may include such discrete layers,and/or substantially intermixed, non-contiguous layers, consistent withthe usage of “layers” previously discussed herein. The device 3900includes first and second substrates 3901 and 3913. A first electrode3902 is disposed upon an inner surface of the first substrate 3901, anda second electrode 3912 is disposed on an inner surface of the secondsubstrate 3913. An active layer 3950 is sandwiched between the twoelectrodes 3902 and 3912. The active layer 3950 includes a mesoporouslayer 3904; first and second photoactive materials 3906 and 3908; acharge transport layer 3910, and several interfacial layers. FIG. 7furthermore illustrates an example device 3900 according to embodimentswherein sub-layers of the active layer 3950 are separated by theinterfacial layers, and further wherein interfacial layers are disposedupon each electrode 3902 and 3912. In particular, second, third, andfourth interfacial layers 3905, 3907, and 3909 are respectively disposedbetween each of the mesoporous layer 3904, first photoactive material3906, second photoactive material 3908, and charge transport layer 3910.First and fifth interfacial layers 3903 and 3911 are respectivelydisposed between (i) the first electrode 3902 and mesoporous layer 3904;and (ii) the charge transport layer 3910 and second electrode 3912.Thus, the architecture of the example device depicted in FIG. 7 may becharacterized as: substrate-electrode-active layer-electrode-substrate.The architecture of the active layer 3950 may be characterized as:interfacial layer-mesoporous layer-interfacial layer-photoactivematerial-interfacial layer-photoactive material-interfacial layer-chargetransport layer-interfacial layer. As noted previously, in someembodiments, interfacial layers need not be present; or, one or moreinterfacial layers may be included only between certain, but not all,components of an active layer and/or components of a device.

A substrate, such as either or both of first and second substrates 3901and 3913, may be flexible or rigid. If two substrates are included, atleast one should be transparent or translucent to electromagnetic (EM)radiation (such as, e.g., UV, visible, or IR radiation). If onesubstrate is included, it may be similarly transparent or translucent,although it need not be, so long as a portion of the device permits EMradiation to contact the active layer 3950. Suitable substrate materialsinclude any one or more of: glass; sapphire; magnesium oxide (MgO);mica; polymers (e.g., PET, PEG, polypropylene, polyethylene, etc.);ceramics; fabrics (e.g., cotton, silk, wool); wood; drywall; metal; andcombinations thereof.

As previously noted, an electrode (e.g., one of electrodes 3902 and 3912of FIG. 7) may be either an anode or a cathode. In some embodiments, oneelectrode may function as a cathode, and the other may function as ananode. Either or both electrodes 3902 and 3912 may be coupled to leads,cables, wires, or other means enabling charge transport to and/or fromthe device 3900. An electrode may constitute any conductive material,and at least one electrode should be transparent or translucent to EMradiation, and/or be arranged in a manner that allows EM radiation tocontact at least a portion of the active layer 3950. Suitable electrodematerials may include any one or more of: indium tin oxide or tin-dopedindium oxide (ITO); fluorine-doped tin oxide (FTO); cadmium oxide (CdO);zinc indium tin oxide (ZITO); aluminum zinc oxide (AZO); aluminum (Al);gold (Au); calcium (Ca); magnesium (Mg); titanium (Ti); steel; carbon(and allotropes thereof); and combinations thereof.

Mesoporous material (e.g., the material included in mesoporous layer3904 of FIG. 7) may include any pore-containing material. In someembodiments, the pores may have diameters ranging from about 1 to about100 nm; in other embodiments, pore diameter may range from about 2 toabout 50 nm. Suitable mesoporous material includes any one or more of:any interfacial material and/or mesoporous material discussed elsewhereherein; aluminum (Al); bismuth (Bi); indium (In); molybdenum (Mo);niobium (Nb); nickel (Ni); silicon (Si); titanium (Ti); vanadium (V);zinc (Zn); zirconium (Zr); an oxide of any one or more of the foregoingmetals (e.g., alumina, ceria, titania, zinc oxide, zircona, etc.); asulfide of any one or more of the foregoing metals; a nitride of any oneor more of the foregoing metals; and combinations thereof.

Photoactive material (e.g., first or second photoactive material 3906 or3908 of FIG. 7) may comprise any photoactive compound, such as any oneor more of silicon (in some instances, single-crystalline silicon),cadmium telluride, cadmium sulfide, cadmium selenide, copper indiumgallium selenide, gallium arsenide, germanium indium phosphide, one ormore semiconducting polymers, and combinations thereof. In certainembodiments, photoactive material may instead or in addition comprise adye (e.g., N719, N3, other ruthenium-based dyes). In some embodiments, adye (of whatever composition) may be coated onto another layer (e.g., amesoporous layer and/or an interfacial layer). In some embodiments,photoactive material may include one or more perovskite materials.Perovskite-material-containing photoactive substance may be of a solidform, or in some embodiments it may take the form of a dye that includesa suspension or solution comprising perovskite material. Such a solutionor suspension may be coated onto other device components in a mannersimilar to other dyes. In some embodiments, solid perovskite-containingmaterial may be deposited by any suitable means (e.g., vapor deposition,solution deposition, direct placement of solid material, etc.). Devicesaccording to various embodiments may include one, two, three, or morephotoactive compounds (e.g., one, two, three, or more perovskitematerials, dyes, or combinations thereof). In certain embodimentsincluding multiple dyes or other photoactive materials, each of the twoor more dyes or other photoactive materials may be separated by one ormore interfacial layers. In some embodiments, multiple dyes and/orphotoactive compounds may be at least in part intermixed.

Charge transport material (e.g., charge transport material of chargetransport layer 3910 in FIG. 7) may include solid-state charge transportmaterial (i.e., a colloquially labeled solid-state electrolyte), or itmay include a liquid electrolyte and/or ionic liquid. Any of the liquidelectrolyte, ionic liquid, and solid-state charge transport material maybe referred to as charge transport material. As used herein, “chargetransport material” refers to any material, solid, liquid, or otherwise,capable of collecting charge carriers and/or transporting chargecarriers. For instance, in PV devices according to some embodiments, acharge transport material may be capable of transporting charge carriersto an electrode. Charge carriers may include holes (the transport ofwhich could make the charge transport material just as properly labeled“hole transport material”) and electrons. Holes may be transportedtoward an anode, and electrons toward a cathode, depending uponplacement of the charge transport material in relation to either acathode or anode in a PV or other device. Suitable examples of chargetransport material according to some embodiments may include any one ormore of: perovskite material; I⁻/I₃ ⁻; Co complexes; polythiophenes(e.g., poly(3-hexylthiophene) and derivatives thereof, or P3HT);carbazole-based copolymers such as polyheptadecanylcarbazoledithienylbenzothiadiazole and derivatives thereof (e.g., PCDTBT); othercopolymers such as polycyclopentadithiophene-benzothiadiazole andderivatives thereof (e.g., PCPDTBT); poly(triaryl amine) compounds andderivatives thereof (e.g., PTAA); Spiro-OMeTAD; fullerenes and/orfullerene derivatives (e.g., C60, PCBM); and combinations thereof. Incertain embodiments, charge transport material may include any material,solid or liquid, capable of collecting charge carriers (electrons orholes), and/or capable of transporting charge carriers. Charge transportmaterial of some embodiments therefore may be n- or p-type active and/orsemi-conducting material. Charge transport material may be disposedproximate to one of the electrodes of a device. It may in someembodiments be disposed adjacent to an electrode, although in otherembodiments an interfacial layer may be disposed between the chargetransport material and an electrode (as shown, e.g., in FIG. 7 with thefifth interfacial layer 3911). In certain embodiments, the type ofcharge transport material may be selected based upon the electrode towhich it is proximate. For example, if the charge transport materialcollects and/or transports holes, it may be proximate to an anode so asto transport holes to the anode. However, the charge transport materialmay instead be placed proximate to a cathode, and be selected orconstructed so as to transport electrons to the cathode.

As previously noted, devices according to various embodiments mayoptionally include an interfacial layer between any two other layersand/or materials, although devices according to some embodiments neednot contain any interfacial layers. Thus, for example, a perovskitematerial device may contain zero, one, two, three, four, five, or moreinterfacial layers (such as the example device of FIG. 7, which containsfive interfacial layers 3903, 3905, 3907, 3909, and 3911). Aninterfacial layer may include a thin-coat interfacial layer inaccordance with embodiments previously discussed herein (e.g.,comprising alumina and/or other metal-oxide particles, and/or atitania/metal-oxide bilayer, and/or other compounds in accordance withthin-coat interfacial layers as discussed elsewhere herein). Aninterfacial layer according to some embodiments may include any suitablematerial for enhancing charge transport and/or collection between twolayers or materials; it may also help prevent or reduce the likelihoodof charge recombination once a charge has been transported away from oneof the materials adjacent to the interfacial layer. Suitable interfacialmaterials may include any one or more of: any mesoporous material and/orinterfacial material discussed elsewhere herein; Al; Bi; In; Mo; Ni;platinum (Pt); Si; Ti; V; Nb; Zn; Zr; oxides of any of the foregoingmetals (e.g., alumina, silica, titania); a sulfide of any of theforegoing metals; a nitride of any of the foregoing metals;functionalized or non-functionalized alkyl silyl groups; graphite;graphene; fullerenes; carbon nanotubes; and combinations thereof(including, in some embodiments, bilayers of combined materials). Insome embodiments, an interfacial layer may include perovskite material.

A device according to the stylized representation of FIG. 7 may in someembodiments be a PV, such as a DSSC, BHJ, or hybrid solar cell. In someembodiments, devices according to FIG. 7 may constitute parallel orserial multi-cell PVs, batteries, hybrid PV batteries, FETs, LEDS,and/or any other device discussed herein. For example, a BHJ of someembodiments may include two electrodes corresponding to electrodes 3902and 3912, and an active layer comprising at least two materials in aheterojunction interface (e.g., any two of the materials and/or layersof active layer 3950). In certain embodiments, other devices (such ashybrid PV batteries, parallel or serial multi-cell PVs, etc.) maycomprise an active layer including a perovskite material, correspondingto active layer 3950 of FIG. 7. In short, the stylized nature of thedepiction of the exemplar device of FIG. 7 should in no way limit thepermissible structure or architecture of devices of various embodimentsin accordance with FIG. 7.

Additional, more specific, example embodiments of perovskite deviceswill be discussed in terms of further stylized depictions of exampledevices. The stylized nature of these depictions, FIGS. 8-9, similarlyis not intended to restrict the type of device which may in someembodiments be constructed in accordance with any one or more of FIGS.8-9. That is, the architectures exhibited in FIGS. 8-9 may be adapted soas to provide the BHJs, batteries, FETs, hybrid PV batteries, serialmulti-cell PVs, parallel multi-cell PVs and other similar devices ofother embodiments of the present disclosure, in accordance with anysuitable means (including both those expressly discussed elsewhereherein, and other suitable means, which will be apparent to thoseskilled in the art with the benefit of this disclosure).

FIG. 8 depicts an example device 4100 in accordance with variousembodiments. The device 4100 illustrates embodiments including first andsecond glass substrates 4101 and 4109. Each glass substrate has an FTOelectrode disposed upon its inner surface (first electrode 4102 andsecond electrode 4108, respectively), and each electrode has aninterfacial layer deposited upon its inner surface: TiO₂ firstinterfacial layer 4103 is deposited upon first electrode 4102, and Ptsecond interfacial layer 4107 is deposited upon second electrode 4108.Sandwiched between the two interfacial layers are: a mesoporous layer4104 (comprising TiO₂); photoactive material 4105 (comprising theperovskite material MAPbI₃); and a charge transport layer 4106 (herecomprising CsSnI₃).

FIG. 9 depicts an example device 4300 that omits a mesoporous layer. Thedevice 4300 includes a perovskite material photoactive compound 4304(comprising MAPbI₃) sandwiched between first and second interfaciallayers 4303 and 4305 (comprising titania and alumina, respectively). Thetitania interfacial layer 4303 is coated upon an FTO first electrode4302, which in turn is disposed on an inner surface of a glass substrate4301. The spiro-OMeTAD charge transport layer 4306 is coated upon analumina interfacial layer 4305 and disposed on an inner surface of agold second electrode 4307.

As will be apparent to one of ordinary skill in the art with the benefitof this disclosure, various other embodiments are possible, such as adevice with multiple photoactive layers (as exemplified by photoactivelayers 3906 and 3908 of the example device of FIG. 7). In someembodiments, as discussed above, each photoactive layer may be separatedby an interfacial layer (as shown by third interfacial layer 3907 inFIG. 7). Furthermore, a mesoporous layer may be disposed upon anelectrode such as is illustrated in FIG. 7 by mesoporous layer 3904being disposed upon first electrode 3902. Although FIG. 7 depicts anintervening interfacial layer 3903 disposed between the two, in someembodiments a mesoporous layer may be disposed directly on an electrode.

Additional Perovskite Material Device Examples

Other example perovskite material device architectures will be apparentto those of skill in the art with the benefit of this disclosure.Examples include, but are not limited to, devices containing activelayers having any of the following architectures: (1) liquidelectrolyte-perovskite material-mesoporous layer; (2) perovskitematerial-dye-mesoporous layer; (3) first perovskite material-secondperovskite material-mesoporous layer; (4) first perovskitematerial-second perovskite material; (5) first perovskitematerial-dye-second perovskite material; (6) solid-state chargetransport material-perovskite material; (7) solid-state charge transportmaterial-dye-perovskite material-mesoporous layer; (8) solid-statecharge transport material-perovskite material-dye-mesoporous layer; (9)solid-state charge transport material-dye-perovskite material-mesoporouslayer; and (10) solid-state charge transport material-perovskitematerial-dye-mesoporous layer. The individual components of each examplearchitecture (e.g., mesoporous layer, charge transport material, etc.)may be in accordance with the discussion above for each component.Furthermore, each example architecture is discussed in more detailbelow.

As a particular example of some of the aforementioned active layers, insome embodiments, an active layer may include a liquid electrolyte,perovskite material, and a mesoporous layer. The active layer of certainof these embodiments may have substantially the architecture: liquidelectrolyte-perovskite material-mesoporous layer. Any liquid electrolytemay be suitable; and any mesoporous layer (e.g., TiO₂) may be suitable.In some embodiments, the perovskite material may be deposited upon themesoporous layer, and thereupon coated with the liquid electrolyte. Theperovskite material of some such embodiments may act at least in part asa dye (thus, it may be photoactive).

In other example embodiments, an active layer may include perovskitematerial, a dye, and a mesoporous layer. The active layer of certain ofthese embodiments may have substantially the architecture: perovskitematerial-dye-mesoporous layer. The dye may be coated upon the mesoporouslayer and the perovskite material may be disposed upon the dye-coatedmesoporous layer. The perovskite material may function as hole-transportmaterial in certain of these embodiments.

In yet other example embodiments, an active layer may include firstperovskite material, second perovskite material, and a mesoporous layer.The active layer of certain of these embodiments may have substantiallythe architecture: first perovskite material-second perovskitematerial-mesoporous layer. The first and second perovskite material mayeach comprise the same perovskite material(s) or they may comprisedifferent perovskite materials. Either of the first and secondperovskite materials may be photoactive (e.g., a first and/or secondperovskite material of such embodiments may function at least in part asa dye).

In certain example embodiments, an active layer may include firstperovskite material and second perovskite material. The active layer ofcertain of these embodiments may have substantially the architecture:first perovskite material-second perovskite material. The first andsecond perovskite materials may each comprise the same perovskitematerial(s) or they may comprise different perovskite materials. Eitherof the first and second perovskite materials may be photoactive (e.g., afirst and/or second perovskite material of such embodiments may functionat least in part as a dye). In addition, either of the first and secondperovskite materials may be capable of functioning as hole-transportmaterial. In some embodiments, one of the first and second perovskitematerials functions as an electron-transport material, and the other ofthe first and second perovskite materials functions as a dye. In someembodiments, the first and second perovskite materials may be disposedwithin the active layer in a manner that achieves high interfacial areabetween the first perovskite material and the second perovskitematerial, such as in the arrangement shown for first and second activematerial 2810 and 2815, respectively, in FIG. 5 (or as similarly shownby p- and n-type material 2618 and 2620, respectively, in FIG. 4).

In further example embodiments, an active layer may include firstperovskite material, a dye, and second perovskite material. The activelayer of certain of these embodiments may have substantially thearchitecture: first perovskite material-dye-second perovskite material.Either of the first and second perovskite materials may function ascharge transport material, and the other of the first and secondperovskite materials may function as a dye. In some embodiments, both ofthe first and second perovskite materials may at least in part serveoverlapping, similar, and/or identical functions (e.g., both may serveas a dye and/or both may serve as hole-transport material).

In some other example embodiments, an active layer may include asolid-state charge transport material and a perovskite material. Theactive layer of certain of these embodiments may have substantially thearchitecture: solid-state charge transport material-perovskite material.For example, the perovskite material and solid-state charge transportmaterial may be disposed within the active layer in a manner thatachieves high interfacial area, such as in the arrangement shown forfirst and second active material 2810 and 2815, respectively, in FIG. 5(or as similarly shown by p- and n-type material 2618 and 2620,respectively, in FIG. 4).

In other example embodiments, an active layer may include a solid-statecharge transport material, a dye, perovskite material, and a mesoporouslayer. The active layer of certain of these embodiments may havesubstantially the architecture: solid-state charge transportmaterial-dye-perovskite material-mesoporous layer. The active layer ofcertain other of these embodiments may have substantially thearchitecture: solid-state charge transport material-perovskitematerial-dye-mesoporous layer. The perovskite material may in someembodiments serve as a second dye. The perovskite material may in suchembodiments increase the breadth of the spectrum of visible lightabsorbed by a PV or other device including an active layer of suchembodiments. In certain embodiments, the perovskite material may also orinstead serve as an interfacial layer between the dye and mesoporouslayer, and/or between the dye and the charge transport material.

In some example embodiments, an active layer may include a liquidelectrolyte, a dye, a perovskite material, and a mesoporous layer. Theactive layer of certain of these embodiments may have substantially thearchitecture: solid-state charge transport material-dye-perovskitematerial-mesoporous layer. The active layer of certain other of theseembodiments may have substantially the architecture: solid-state chargetransport material-perovskite material-dye-mesoporous layer. Theperovskite material may serve as photoactive material, an interfaciallayer, and/or a combination thereof.

Some embodiments provide BHJ PV devices that include perovskitematerials. For example, a BHJ of some embodiments may include aphotoactive layer (e.g., photoactive layer 2404 of FIG. 3), which mayinclude one or more perovskite materials. The photoactive layer of sucha BHJ may also or instead include any one or more of the above-listedexample components discussed above with respect to DSSC active layers.Further, in some embodiments, the BHJ photoactive layer may have anarchitecture according to any one of the exemplary embodiments of DSSCactive layers discussed above.

In some embodiments, any PV or other like device may include an activelayer according to any one or more of the compositions and/orarchitectures discussed above. As another example embodiment, an activelayer including perovskite material may be included in amulti-photoactive-layer PV cell, such as either or both of the first andsecond photoactive layers 3701 and 3705 of the exemplary cell shown inthe stylized diagram of FIG. 6. Such a multi-photoactive-layer PV cellincluding an active layer with perovskite material could furthermore beincorporated within a series of electrically coupledmulti-photoactive-layer PV cells.

In some embodiments, any of the active layers including perovskitematerials incorporated into PVs or other devices as discussed herein mayfurther include any of the various additional materials also discussedherein as suitable for inclusion in an active layer. For example, anyactive layer including perovskite material may further include aninterfacial layer according to various embodiments discussed herein(such as, e.g., a thin-coat interfacial layer). By way of furtherexample, an active layer including perovskite material may furtherinclude a light harvesting layer, such as Light Harvesting Layer 1601 asdepicted in the exemplary PV represented in FIG. 2.

Formulation of the Perovskite Material Active Layer

As discussed earlier, in some embodiments, a pervoskite material in theactive layer may have the formulation CMX_(3-y)X′_(y) (0≧y≧3), where: Ccomprises one or more cations (e.g., an amine, ammonium, a Group 1metal, a Group 2 metal, and/or other cations or cation-like compounds);M comprises one or more metals (e.g., Fe, Cd, Co, Ni, Cu, Hg, Sn, Pb,Bi, Ge, Ti, Zn, and Zr); and X and X′ comprise one or more anions. Inone embodiment, the perovskite material may comprise CPbI_(3-y)Cl_(y).In certain embodiments, the perovskite material may be deposited as anactive layer in a PV device by, for example, drop casting, spin casting,slot-die printing, screen printing, or ink-jet printing onto a substratelayer using the steps described below.

First, a lead halide precursor ink is formed. An amount of lead halidemay be massed in a clean, dry vial inside a glove box (i.e., controlledatmosphere box with glove-containing portholes allows for materialsmanipulation in an air-free environment). Suitable lead halides include,but are not limited to, lead (II) iodide, lead (II) bromide, lead (II)chloride, and lead (II) fluoride. The lead halide may comprise a singlespecies of lead halide or it may comprise a lead halide mixture in aprecise ratio. In certain embodiments, the lead halide mixture maycomprise any binary, ternary, or quaternary ratio of 0.001-100 mol % ofiodide, bromide, chloride, or fluoride. In one embodiment, the leadhalide mixture may comprise lead (II) chloride and lead (II) iodide in aratio of about 10:90 mol:mol. In other embodiments, the lead halidemixture may comprise lead (II) chloride and lead (II) iodide in a ratioof about 5:95, about 7.5:92.5, or about 15:85 mol:mol.

A solvent may then be added to the vial to dissolve the lead solids toform the lead halide precursor ink. Suitable solvents include, but arenot limited to, dry dimethylformamide, dimethylsulfoxide (DMSO),methanol, ethanol, propanol, butanol, tetrahydrofuran, formamide,pyridine, pyrrolidine, chlorobenzene, dichlorobenzene, dichloromethane,chloroform, and combinations thereof. In one embodiment, the lead solidsare dissolved in dry dimethylformamide (DMF). The lead solids may bedissolved at a temperature between about 20° C. to about 150° C. In oneembodiment, the lead solids are dissolved at about 85° C. The leadsolids may be dissolved for as long as necessary to form a solution,which may take place over a time period up to about 72 hours. Theresulting solution forms the base of the lead halide precursor ink. Insome embodiments, the lead halide precursor ink may have a lead halideconcentration between about 0.001M and about 10M. In one embodiment, thelead halide precursor ink has a lead halide concentration of about 1 M.In some embodiments, the lead halide precursor ink may further comprisean amino acid (e.g., 5-aminovaleric acid, histidine, glycine, lycine),an amino acid hydrohalide (e.g., 5-amino valeric acid hydrochloride), anIFL surface-modifying (SAM) agent (such as those discussed earlier inthe specification), or a combination thereof.

The lead halide precursor ink may then be deposited on the desiredsubstrate. Suitable substrate layers may include any of the substratelayers identified earlier in this disclosure. As noted above, the leadhalide precursor ink may be deposited through a variety of means,including but not limited to, drop casting, spin casting, slot-dieprinting, screen printing, or ink-jet printing. In certain embodiments,the lead halide precursor ink may be spin-coated onto the substrate at aspeed of about 500 rpm to about 10,000 rpm for a time period of about 5seconds to about 600 seconds. In one embodiment, the lead halideprecursor ink may be spin-coated onto the substrate at about 3000 rpmfor about 30 seconds. The lead halide precursor ink may be deposited onthe substrate at an ambient atmosphere in a humidity range of about 0%relative humidity to about 50% relative humidity. The lead halideprecursor ink may then be allowed to dry in a substantially water-freeatmosphere, i.e., less than 20% relative humidity, to form a thin film.

The thin film can then be thermally annealed for a time period up toabout 24 hours at a temperature of about 20° C. to about 300° C. In oneembodiment, the thin film may be thermally annealed for about tenminutes at a temperature of about 50° C. The perovskite material activelayer may then be completed by a conversion process in which theprecursor film is submerged or rinsed with a solution comprising asolvent or mixture of solvents (e.g., DMF, isopropanol, methanol,ethanol, butanol, chloroform chlorobenzene, dimethylsulfoxide, water)and salt (e.g., methylammonium iodide, formamidinium iodide, guanidiniumiodide, 1,2,2-triaminovinylammonium iodide, 5-aminovaleric acidhydroiodide) in a concentration between 0.001M and 10M. In certainembodiments, the thin films can also be thermally post-annealed in thesame fashion as in the first line of this paragraph.

Purification of Ammonium Iodide

As discussed earlier, in some embodiments, the precursor film for theperovskite material active layer may be submerged or rinsed with asolution comprising a solvent or mixture of solvents, and a saltincluding, but not limited to, methylammonium iodide, formamidiniumiodide, guanidinium iodide. Described below is a synthetic procedure formethyl ammonium iodide (MAI). A similar procedure can be applied toguanidinium iodide (GAI), formamidinium iodide (FAI), amino acid iodide,or any halide (e.g., iodine, bromine, chlorine, or fluorine) saltthereof.

A molar excess of methyl amine in methanol is added to an aqueoushydroiodic (HI) solution in a vessel. In one embodiment, the methylamine has a concentration of about 9.8 M, although suitableconcentrations may range from about 0.001M to about 12M. In oneembodiment, the HI solution has a concentration of about 57%, althoughsuitable concentrations may range from about 1% to about 100%. Anysuitable vessel can be used, including but not limited to, a roundbottom flask, a beaker, an Erlenmeyer flask, a Schlenk flask or anyglass vessel. The reaction is performed under an inert atmosphere freeof oxygen with dropwise addition with stirring. In one embodiment, thereaction takes place at a temperature of about 0° C., although thereaction can also take place at a temperature as low as about −196° C.or as high as about 100° C. After the completion of the methyl amineaddition, the solution is allowed to mix and warm to room temperatureover a 2 hour period. In some embodiments, the solution can be warmed toroom temperature in as little as about 1 minute or as long as about 72hours. After the completion of the reaction, the solvent is removedusing a vacuum. A solid remains, which may be red or orange in color.This solid is an impure form of methyl ammonium iodide, in particular amixture that comprises methyl ammonium iodide, excess startingmaterials, and/or reaction byproducts.

A non-polar or slightly polar solvent (e.g., diethyl ether) is thenadded to the impure methyl ammonium iodide, and the mixture is sonicatedfor about 30 minutes in the dark before decanting the liquid. In someembodiments, the solution can be sonicated for any length of time up toabout 12 hours. This diethyl ether washing step may be repeated anynumber of times until the solid becomes colorless or slightly yellow. Inone embodiment, the diethyl ether washing step is repeated for a totalof three times. This produces a more pure form of methyl ammoniumiodide.

The methyl ammonium iodide is then dissolved in minimum solvent ethanolvolume in a sonicator at a temperature between about 20° C. to about150° C. In one embodiment, the temperature is about 60° C. Suitablesolvents include methanol, ethanol, propanol, butanol or other polarsolvents. In one embodiment, the solvent comprises ethanol. Once fullydissolved, the solution is cooled to room temperature over a time periodof about 30 minutes, and then is layered with an equal volume (toethanol) of diethyl ether. In other embodiments, the ratio of ethanol todiethyl ether may range from about 1:10 to about 10:1 by volume. Thevessel is then purged with an inert gas (e.g., argon or nitrogen), andthen placed in a cold, dark place. In some embodiments, the vessel maybe placed in an environment with a temperature of about −196° C. toabout 25° C. In one embodiment, the vessel may be placed in arefrigerator. The vessel may be left in the cold, dark place for a timeperiod of about 1 hour to about 168 hours. In one embodiment, the vesselmay be left in the cold, dark place for about 14 hours. The resultingcolorless crystalline solid is recovered by a suitable method (e.g.,vacuum filtration, gravity filtration, or centrifuge), and subsequentlywashed with a cold non-polar or slightly polar solvent (e.g., diethylether) and dried. In some embodiments, the crystalline solid may bewashed once, twice, or more times. The crystalline may be dried inambient air or by any suitable equipment, including but not limited to,a vacuum oven, a convection oven, a furnace, a vacuum desiccator, or avacuum line. In one embodiment, solid is dried for about 14 hours atabout 40° C. However, the solid may be dried for a period of time fromabout 1 hour to about 168 hours and at a temperature from about 20° C.to about 200° C.

Therefore, the present invention is well adapted to attain the ends andadvantages mentioned as well as those that are inherent therein. Theparticular embodiments disclosed above are illustrative only, as thepresent invention may be modified and practiced in different butequivalent manners apparent to those skilled in the art having thebenefit of the teachings herein. Furthermore, no limitations areintended to the details of construction or design herein shown, otherthan as described in the claims below. It is therefore evident that theparticular illustrative embodiments disclosed above may be altered ormodified and all such variations are considered within the scope andspirit of the present invention. In particular, every range of values(of the form, “from about a to about b,” or, equivalently, “fromapproximately a to b,” or, equivalently, “from approximately a-b”)disclosed herein is to be understood as referring to the power set (theset of all subsets) of the respective range of values, and set forthevery range encompassed within the broader range of values. Also, theterms in the claims have their plain, ordinary meaning unless otherwiseexplicitly and clearly defined by the patentee.

1-30. (canceled)
 31. A method comprising the steps of: preparing abismuth halide precursor ink, wherein preparing a bismuth halideprecursor ink comprises the steps of: introducing a bismuth halide intoa vessel; introducing a first solvent to the vessel; and contacting thebismuth halide with the first solvent to dissolve the lead halide toform the lead halide precursor solution; depositing the bismuth halideprecursor ink onto a substrate; drying the bismuth halide precursor inkto form a thin film; annealing the thin film; and rinsing the thin filmwith a second solvent and a salt selected from the group consisting ofmethylammonium halide, formamidinium halide, guanidinium halide,1,2,2-triaminovinylammonium halide, and 5-aminovaleric acid hydrohalide.32. The method of claim 31, wherein annealing the thin film occurs forbetween about 5 to about 30 minutes at a temperature between about 40°C. to about 60° C.
 33. The method of claim 31, wherein the salt isselected from the group consisting of methylammonium iodide,formamidinium iodide, guanidinium iodide, 1,2,2-triaminovinylammoniumiodide, and 5-aminovaleric acid hydroiodide.
 34. The method of claim 31,wherein the first solvent is selected from the group consisting of drydimethylformamide, dimethylsulfoxide (DMSO), methanol, ethanol,propanol, butanol, tetrahydrofuran, formamide, pyridine, pyrrolidine,chlorobenzene, dichlorobenzene, dichloromethane, chloroform, andcombinations thereof.
 35. The method of claim 31, wherein contacting thebismuth halide with the solvent to dissolve the bismuth halide occursbetween about 20° C. to about 150° C.
 36. The method of claim 31,wherein contacting the bismuth halide with the solvent to dissolve thebismuth halide occurs at about 85° C.
 37. The method of claim 31,wherein the bismuth halide precursor ink has a concentration of thebismuth halide between about 0.001M and about 10M.
 38. The method ofclaim 31, wherein depositing the bismuth halide precursor ink onto thesubstrate occurs by drop casting, spin casting, slot-die printing,screen printing, or ink-jet printing.
 39. The method of claim 31,wherein annealing the thin film occurs for up to 24 hours at atemperature between about 20° C. to about 300° C.
 40. The method ofclaim 31, wherein annealing the thin film occurs for about ten minutesat a temperature of about 50° C.
 41. The method of claim 31, wherein thesecond solvent selected from the group consisting of dimethylformamide,isopropanol, methanol, ethanol, butanol, chloroform, chlorobenzene,dimethylsulfoxide, water, and combinations thereof.
 42. The method ofclaim 31, wherein the salt comprises formamidinium iodide.
 43. Themethod of claim 42, wherein the salt is dissolved in the second solventin a concentration of between about 0.001M and about 10M.
 44. The methodof claim 31, wherein the salt comprises methylammonium iodide.
 45. Themethod of claim 31, wherein rinsing the thin film comprises at leastpartial submersion in the second solvent.
 46. A perovskite materialprepared by a process comprising the steps of: preparing a bismuthhalide precursor ink, wherein preparing a bismuth halide precursor inkcomprises the steps of: introducing a bismuth halide into a vessel;introducing a first solvent to the vessel; and contacting the bismuthhalide with the first solvent to dissolve the bismuth halide; depositingthe bismuth halide precursor ink onto a substrate; drying the bismuthhalide precursor ink to form a thin film; annealing the thin film; andrinsing the thin film with a second solvent and a salt selected from thegroup consisting of methylammonium halide, formamidinium halide,guanidinium halide, 1,2,2-triaminovinylammonium halide, and5-aminovaleric acid hydrohalide to form the perovskite material.
 47. Theperovskite material of claim 46, wherein annealing the thin film occursfor between about 5 to about 30 minutes at a temperature between about40° C. to about 60° C.
 48. The perovskite material of claim 46, whereinthe salt is selected from the group consisting of methylammonium iodide,formamidinium iodide, guanidinium iodide, 1,2,2-triaminovinylammoniumiodide, and 5-aminovaleric acid hydroiodide.
 49. The perovskite materialof claim 46, wherein the first solvent is selected from the groupconsisting of dry dimethylformamide, dimethylsulfoxide (DMSO), methanol,ethanol, propanol, butanol, tetrahydrofuran, formamide, pyridine,pyrrolidine, chlorobenzene, dichlorobenzene, dichloromethane,chloroform, and combinations thereof.
 50. The perovskite material ofclaim 46, wherein contacting the bismuth halide with the solvent todissolve the bismuth halide occurs between about 20° C. to about 150° C.51. The perovskite material of claim 46, wherein contacting the bismuthhalide with the solvent to dissolve the bismuth halide occurs at about85° C.
 52. The perovskite material of claim 46, wherein the bismuthhalide precursor ink has a concentration of the bismuth halide betweenabout 0.001M and about 10M.
 53. The perovskite material of claim 46,wherein depositing the bismuth halide precursor ink onto the substrateoccurs by drop casting, spin casting, slot-die printing, screenprinting, or ink-jet printing.
 54. The perovskite material of claim 46,wherein annealing the thin film occurs for up to 24 hours at atemperature between about 20° C. to about 300° C.
 55. The perovskitematerial of claim 46, wherein annealing the thin film occurs for aboutten minutes at a temperature of about 50° C.
 56. The perovskite materialof claim 46, wherein the second solvent selected from the groupconsisting of dimethylformamide, isopropanol, methanol, ethanol,butanol, chloroform chlorobenzene, dimethylsulfoxide, water, andcombinations thereof.
 57. The perovskite material of claim 46, whereinthe salt comprises formamidinium iodide.
 58. The perovskite material ofclaim 57, wherein the salt is dissolved in the second solvent in aconcentration of between about 0.001M and about 10M.
 59. The perovskitematerial of claim 46, wherein the salt comprises methylammonium iodide.60. The perovskite material of claim 46, wherein rinsing the thin filmcomprises at least partial submersion in the second solvent.